This invention relates to a process for the production of flame-retardant polyurethane foamed products by mixing and reacting an acid boron salt forming compound, a polyol, a low molecular weight compound containing 1 or more active hydrogens that will react with a polyisocyanate and in the presence of an organo-metal urethane catalyst.
The production of polyurethane products are well known in the Arts and many types of flame-retardant chemicals have been used in the process. It is also known in the Arts that salts of boric acid are useful as a flame-retardant but require the addition of other flame-retardants, therefore they are not very useful. In the novel process of this invention, only small amount of acid boron compounds are necessary to produce a flame-retardant product because the molecules of the boric acid are small and very well distributed throughout the product. The problem in the past encountered with the use of boric acid in the production of polyurethane foams was that it is an acidic compound, therefore a negative catalyst and interferes with the curing of the polyurethane foams. The curing time is so prolonged in most formulation that the foam collapses and it takes days for the mixture to cure. This prolonged curing time is especially pronounced in the production of flexible foams utilizing polyols with a hydroxyl number of less than 200 and tolylene diisocyanates or polymeric MDI. In the production of rigid polyurethane foams using polyols with a hydroxyl no. above 300, polymeric MDI and boric acid there is a slowing down of the curing process but a foam product can be produced without using a low molecular weight compound or an organotin catalyst but a better foam is produced when using them.
I have discovered that the negative catalytic effect of boric acid may be over come by the utilization of a low molecular weight compound that contains active hydrogens which will rapidly react with a polyisocyanate in the presence of an organo-metal polyurethane catalyst. The anhydrous boric acid powder will also promote the production of a gas which foams the polyurethane product. The exact chemical reaction is not known but it appears that some of the boric acid is esterified with the hydroxyl radicals and water is produced in the process. The water reacts with the isocyanate radical to produce CO.sub.2 which acts as a foaming agent. When boric acid is heated to above 100.degree. C., water is given off. The need to use halogenated blowing agents is greatly reduced. In the process of this invention, low cost and readily available compounds, such as boric acid, are utilized and there is an improvement in the cost of the product, in the amount of flame-retardant needed, and in the production of inexpensive flame-retardant compounds. It takes an amount at least 3 to 5 times more when the salt of acid boron compound is added to the reacting mixture instead of boric acid to produce flame-retardant polyurethane products. The flame-retardant boric acid of this invention is less expensive and at least equal to, or better than, the commercially available flame-retardant agents for polyurethane products in flame-retardant properties.
The polyurethane products may contain as little as 7 percent by weight of boric acid and have good flame-retardant properties. The amount of acid boron compound that would normally be used ranges from 7 percent to 25 percent of the reactive mixture to produce flame-retardant polyurethane products.
In the production of flexible polyurethane-boric acid foams it is necessary to use a low molecular weight compound containing an active hydrogen and an organo-metal urethane catalyst with the organic triol and polyisocyanate in order to produce a useful flexible foam. Other urethane catalyst such as amine catalyst may also be used in some products.